flowerbug
Garden Master
My first thought would be cutworms, some varieties do that. Have you tried digging around the plant to check for them? When I was talking to the plant guy at the extension office he said beetles could do that but I didn't ask which beetles. When I applied a pesticide that activity stopped.
I suppose rats could do that (hard to fence rats out) but the one time I could identify the culprit as a rat (she died) she would eat a couple of plants to the ground each night, starting at the end of the row nearest the hiding place and just working her way down. Of course it could be something else but why would a rodent bite off a leaf and drop it? Then do it again? If they are not going to eat them why spend the energy and time to bite them off and drop them? I'm sure they could, sometimes they just seem to enjoy being destructive. But my first thoughts go to the insect world.
no other plants have been touched along there since then. when it happened the first thing i did was look around for cutworm hiding place and made sure that any holes in the ground were stirred up and then plugged. just one of those mysteries. like maybe it was a bird going for a bug on the stem and it missed twice or something odd like that... no marks in the surrounding soil though. i guess sometimes a bit of a mystery is what keeps us on our toes?